Power Management Controller - Compaq Armada e500 Series Reference Manual

The adapter simply outputs 19 volts at 50 watts continuous, 60 watts peak (2.8 amps
output max). The DC input is a simple two-wire (ground and power) connection, and
may be connected to a wide number of sources. Primary support is given to the airline
adapter and automotive adapter, but consideration is given that virtually any supply may
be connected to the input.
The AC/DC or DC input may be turned off by control of the CPU, by turning off a FET
under control of the MSIO. This feature is to perform battery calibration.

Power Management Controller

The system power management is performed by the 8051 microcontroller that is
integrated in the MSIO Super I/O device. The controller monitors the batteries, power,
standby, and keyboard Fn switches, controls battery charging, provides a battery fuel
gauge to the system, and indirectly turns the DC/DC converter On and OFF. The
controller interfaces to the system logic through 14 mailbox registers in the MSIO.
The intelligence in the constant voltage circuit pivots around the voltage and current
sensing logic. The circuitry consists of two voltage level comparators, two current level
load comparators, an AC adapter charge/discharge FET pair and logic for battery charge
and arbitration. The purpose of the voltage and current sensing circuitry is to:
Detect if external power is present (AC or DC input) and initiate battery discharge
Monitor current into the System and disable battery charge when the AC/DC limit is
exceeded
Charger presence (AC presence) is detected with a voltmeter detecting 17.5 volts or
greater on the power rail input. The output of the AC-present logic goes to the MSIO
"Charger Present" input and also may assert MBAT. The "Current Flow" ammeter
makes sure that a battery stack voltage of 17.5 volts will NOT falsely assert "Charger
Present."
A DC input jack may be present on the computer, intended to be supplied by either an
airline adapter or automotive adapter. The DC-present voltmeter checks for an external
voltage input of 12 VDC or greater. When an external source of voltage is applied
between 12 and 17.5 volts, the system recognizes the external input but will not allow
the battery to charge.
Hysterisis is built into the comparator, so that simple connection to a car's electrical
supply will not cause the DC presence to be lost during a sag in the line (for instance,
during cranking of the engine).
The "Current Flow" ammeter prevents the battery from backfeeding the AC/DC or DC
input jack. It prevents the battery voltage from falsely indicating either "Charger
present" or "DC-present." This current direction circuit has the advantage of low power
and heat loss using an active circuit. The system is protected from a failure on the
charger or DC input.
The ammeter consists of a comparator across a 50 milliohm resistor, R16. The output of
this comparator is not read anywhere by the system, but acts to enable FET Q4. With Q4
turned off, the battery voltage VBAT cannot backfeed to the VADP rail.
Power Supply 9-5